The present invention generally relates to a method and apparatus for rectifying motion. More specifically, the present invention relates to a method and apparatus for converting reciprocating motion into single direction rotational motion. The present invention further relates to an exercise machine that incorporates the apparatus for converting reciprocating motion into single direction rotational motion.
Devices for converting reciprocating motion into single direction rotational motion are disclosed in the art. For example, the mechanical apparatus for providing upper body exercise that is described in U.S. Pat. No. 4,923,193 generates single direction rotational motion that is derived from reciprocating motion. The apparatus of this patent relies upon a chain-based mechanism for converting reciprocating motion to single direction rotational motion.
The mechanism of U.S. Pat. No. 4,923,193 provides a solution to the problem of "dead points" that arise when a crank arm is connected to a pulley in conventional fashion. However, the need to employ a chain or other type of flexible mechanism, such as a continuous belt, in the mechanism of Pat. No. 4,923,193 produces an undesirable byproduct, namely, an unpleasant jerking sensation to the user stemming from chordal action of the chain. The jerking sensation is caused by changing velocities of sections or linkages of the belt or chain that are associated with changes in the effective radius of action, the well known "chordal effect," during operation of the exercise machine.
U.S. Pat. No. 5,542,893 solves the undesirable jerking sensation problems by replacing the flexible belt or chain with a rack and pinion system. In apparatus 10 of U.S. Pat. No. 5,542,893, as depicted in prior art FIG. 1, a pair of pinions 12, 13 are mounted on respective one-way clutches 14, 15. The one-way clutches 14, 15 are mounted onto a rotatable shaft 16 that is mounted within a frame (not shown).
The pinions 12, 13 each include a plurality of teeth 18 that are spaced about the radius of each pinion 12, 13. The apparatus of U.S. Pat. No. 5,542,893 also includes a yoke 20 and a pair of attached racks 22, 24 that are attached to opposing sides 26, 28 of the yoke 20. The racks 22, 24 each include a plurality of gear teeth 30, 32, respectively, that engage the teeth 18 of the pinions 12, 13, respectively. Rotation of the pinions 12, 13 and the associated one-way clutches 14, 15 in the same direction about the shaft 16 imparts power to the shaft 16 when the speed of the pinions 12, 13 exceeds the rotational speed of the shaft 16.
The one-way clutches 14, 15 are each fixedly mounted, and are each oriented, on the shaft 16 so that the clutches 14, 15, when engaged, each impart power to the shaft 16 in the same rotational direction about the shaft 16, so long as the rotational speed of the clutch 14 or the clutch 15 exceeds the rotational speed of the shaft 16. The clutches 14, 15 do not each impart power to the shaft 16 at the same time. Rather, when the yoke 20 and attached rack 22 are moved in a primary direction to engage the pinion 12, the clutch 14 imparts power to the shaft 16 to increase the rotational speed of the shaft 16 so long as the speed of the rack 22 is greater than the speed of the shaft 16, whereas the clutch 15 freewheels with respect to the shaft 16. Conversely, when the yoke 20 and attached rack 24 are moved in a reciprocal direction to the primary direction, the rack 24 engages the pinion 13 and the clutch 15 imparts power to the shaft 16 to increase the speed of the shaft 16 so long as the speed of the rack 24 in the reciprocal direction is faster than the speed of the rotatable shaft 16, whereas the clutch 14 freewheels with respect to the shaft 16. Thus, whenever the yoke 20 and rack 22 are moving in the primary direction to engage the pinion 12, the one-way clutch 15 is free wheeling. Conversely, whenever the yoke 20 and rack 24 are moved in the reciprocal direction to the primary direction to engage the pinion 13, in place of "the one-way clutch 15 is free wheeling."
This structure of the motion conversion apparatus of U.S. Pat. No. 5,542,893 avoids the undesirable jerking sensation associated with the chain-based mechanism of U.S. Pat. No. 4,923,193. However, it has been discovered that operation of this apparatus 10 that is disclosed in U.S. Pat. No. 5,542,893 creates some frictional forces that undesirably reduce the efficiency of the apparatus 10 and can cause significant wear of some system 10 components.
Specifically, when the yoke 20 and rack 24 are moved in the primary direction, radial forces acting in the direction of arrow A create a moment in the direction of arrow B that tends to cause the yoke 20 to rotate in the direction of arrow B. This movement of the yoke 20 in the direction of arrow B is arrested by contact between surface 34of the yoke 20 and surface 36 of the pinion 13 and by contact between the surface 38 of the yoke 20 and surface 40 of the pinion 12.
This contact between the surfaces 34, 36 and between the surfaces 38, 40 does prevent the teeth 30 of the rack 22 from becoming disengaged with the teeth 18 of the clutch 14. However, the enhanced contact between the surfaces 34, 36 and between the surfaces 38, 40 is nevertheless undesirable due to increased frictional forces that arise from this rubbing contact of the surfaces 34, 36 and the surfaces 38, 40. Furthermore, the potential for significant wear exists where the surfaces 34, 36 contact each other and where the surfaces 38, 40 contact each other. This wear and friction concern is especially pronounced where the surfaces 38, 40 contact each other, since the yoke 20 and the pinion 12 are moving in opposite directions at a net speed of two times the primary speed where the surfaces 38, 40 contact each other.
A similar friction and wear problem arises when the yoke 20 and rack 24 are moved in a direction that is reciprocal to the primary direction. Here, a separation force in the direction of arrow C arises due to the interaction of the gear teeth 32 of the rack 24 and the gear teeth 18 of the pinion 13. This force in the direction of arrow C creates a radial moment in the direction of arrow D that tends to cause the yoke 20 to rotate in the direction of arrow D. This rotation pressures the surfaces 34, 36 against each other and also pressures the surfaces 38, 40 against each other.
This contact between the surfaces 34, 36 and between the surfaces 38, 40 does prevent the teeth 32 of the rack 24 from becoming disengaged with the teeth 18 of the pinion 13. However, the enhanced contact between the surfaces 34, 36 and between the surfaces 38, 40 is nevertheless undesirable due to increased frictional forces that arise from this rubbing contact of the surfaces 34, 36 and the surfaces 38, 40. Furthermore, the potential for significant wear exists where the surfaces 34, 36 contact each other and where the surfaces 38, 40 contact each other When the yoke 20 and rack 24 are moved in the reciprocal direction to the primary direction, the enhanced contact is most problematic at the surfaces 34, 36, since such reciprocal direction movement causes the surfaces 34, 36 to move against each other in opposite directions at a net speed of two times the speed of the yoke 20 in the reciprocal direction.
A solution is needed to the surface contact problems that arise when the yoke 20 tends to rotate in the direction of arrow B during movement of the yoke 20 in the primary direction and the related tendency of the yoke 20 to move in the direction of arrow D during movement of the yoke 20 in the reciprocal direction. Such a solution is desirable because the enhanced pressure at the surfaces 34, 36 and at the surfaces 38, 40 due to the rotation tendency of the yoke 20 in the direction of arrow B or in the direction of arrow D creates the potential for enhanced wear where the surfaces 34, 36 contact each other and where the surfaces 38, 40 contact each other. Additionally, the enhanced frictional forces at the surfaces 34, 36 and at the surfaces 38, 40 significantly reduce the efficiency at which motion in the primary and the reciprocal direction is converted to single direction rotational motion via the pinions 12, 13 and respective one-way clutches 14, 15.